Preparation of 5-aroyl-pyrroles and intermediates therefor

ABSTRACT

A process of preparing certain 5-aroyl-pyrrole-2-alkanoic acid derivatives using phosgene and certain 5-unsubstituted pyrroles as starting materials, and certain novel 5-chlorocarbonyl-pyrrole precursors.

United States Patent 19] Carson [451 Nov. 5, 1974 PREPARATION OF S-AROYL-PYRROLES AND INTERMEDIATES THEREFOR [75] Inventor: John Robert Carson, Norristown,

[73] Assignee: McNeil Laboratories, Inc., Ft.

Washington, Pa.

[22] Filed: Aug. 3, 1972 [21] Appl. No.: 277,845

OTHER PUBLICATIONS Mozheiko et aL, Chem. Abs. 69: 287252, (1968), abs.

of USSR Pat. 214,307.

Ottenheym et al., Chem. Abs. 60: 6756d, (1964), abs. of Germ. 1,157,210.

Wagner et al., Synthetic Organic Chemistry, (I953), pp. 333-34.

Primary Examiner-Joseph A. Narcavagc Attorney. Agent, or Firm-Salvatorc R. (onto [57] ABSTRACT A process of preparing certain 5-aroyl-pyrrole-2- alkanoic acid derivatives using phosgenc and certain S-unsubstituted pyrroles as starting materials, and certain novel 5-chlorocarbonyl-pyrrole precursors.

15 Claims, No Drawings PREPARATION OF S-AROYL-PYRROLES AND INTERMEDIATES THEREFOR BACKGROUND OF THE INVENTION 5-Aroyl-pyrroles have been made heretofore by Friedel-Crafts acylation procedures (see Belgian Pat. 'No. 762,060). The subject process reacts phosgene with appropriate 5-unsubstituted pyrroles and the thusobtained 5-chlorocarbonyl-pyrroles are then transformed into the desired 5-aroyl-pyrroles.

DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention relates to a novel method of preparing 5-aroyl-pyrrole-2-alkanoic acid derivatives of the for-' wherein R represents a member selected from the group consisting of hydrogen and lower alkyl, preferably methyl;

R, represents lower alkyl, preferably methyl; R represents a member selected from the group consisting of CN, COO(lower alkyl) and COOH; and

Ar represents a member selected from the group consisting of phenyl and phenyl substituted with one or more members selected from the group consisting of halo, lower alkyl, lower alkoxy, trifluoromethyl and methylthio; provided that, when said R is lower alkyl, then said R is other than CN.

As used herein, lower alkyl" and lower alkoxy may be straight or branch chained and have from I to about 6 carbon atoms, such as, for example, methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl and the like alkyls, and, respectively, the corresponding alkoxys such as, for example, methoxy, ethoxy, propoxy, isopropoxy, etc.; and the term halo" stands forchloro, bromo, fluoro and iodo. Among the preferred substituted phenyls embraced by the symbol Ar are monodiand tri-substituted phenyls, particularly the monoand di-substituted phenyls, wherein each substituent is a member selected from the group consisting of halo, lower alkyl, lower alkoxy, trifluoromethyl and methylthio.

The compounds of formula (I) possess antiinflammatory activity (see Belgian Pat. No. 762,060).

The following novel and advantageous process may be used to prepare said compounds. The symbol Z denotes the nitrile and ester forms of (I), that is, Z represents a member selected from the group consisting of CN and COO(lower alkyl).

According to the instant process, phosgene (II) is reacted with an appropriate S-unsubstituted pyrrole of formula (III) in a suitable inert aprotic solvent such as, for example, an aromatic hydrocarbon, e.g., benzene, toluene, xylene and the like; an ether, e.g., diethyl ether, tetrahydrofuran, dioxane and the like; and a ha logenated lower alkane, e.g., chloroform, methylene chloride, 1,2-dichloroethane and the like. If desired, an

appropriate halogen acid acceptor, e.g., an amine base such as triethylamine, may be employed as a scavenger to pick up the HCl that is eliminated during the course of the reaction. Temperatures ranging from about 0C. to about C. are generally employed. Although stoichiometric quantities of the two reactants may suitably be employed, a slight molar excess (about 10 percent) of phosgene is preferred.

The thus-obtained S-chlorocarbonyl-pyrrole of formula (IV) is then treated with either:

i. an appropriate aryl magnesium halide (Grignard reagent), e.g., a compound of the formula: ArMgBr, wherein Ar is as previously described, in the presence of a catalytic amount of a transition metal halide, such as, for example ZnCl CdCI FeCl CoCl (CuBr) and the low temperatures, preferably below 50C.; or

ii. an appropriate aryl transition metal compound of the formula: (Ar),,M, wherein Ar is as previously described, M is a transition metal selected from the group consisting of copper, 'zinc and cadmium, and n is an integer equal to the valence of the particular transition metal salt employed, ambient temperatures generally being employed;

in a suitable aprotic solvent preferably an aromatic hydrocarbon or ether mentioned previously, in order to prepare the desired S-aroyl-pyrrole nitriles and esters of formula (V). The (Ar),,M compounds are conveniently prepared in situ by adding a transition metal halide, e.g., cadmium chloride, zinc chloride and the like, to a solution of an appropriate aryl magnesium halide Grignard reagent.

Standard nitrile-to-acid and ester-to-acid hydrolysis procedures are then employed in order to transform the respective nitrile and ester functions to the corresponding acid form of formula (I). The foregoing reactions may be schematically illustrated as follows:

coon I N/ 0100 N -ornz l l.

The 5-chlorocarbonyl-pyrroles of formula (IV) are novel compounds and, in view of their utility as intermediates in the synthesis of formula (I) compounds, they constitute an additional feature of this invention as does the method of making same.

The following examples are intended to illustrate, but not to limit, the scope of the present invention. Unless otherwise stated, all parts are by weight.

EXAMPLE I 5-Chlorocarbonyl-l-methylpyrrole-2-acetonitrile 2-acetonitrile in 50 ml. of ether is added to a solution of 5.85 g. (0.06 mole) of phosgene in 100 ml. of ether. The solution is allowed to stand at room temperature for 18 hours. The solvent is evaporated in vacuo and the residue is recrystallized from ether to give 5.1 g. of -chlorocarbonyl-1-methylpyrrole-2 acetonitrile as a red solid, m.p. 7880C.

EXAMPLE II EXAMPLE III Ethyl 5-chlorocarbonyl-l,4-dimethylpyrrole-Z-acetate A solution of 5.0 g. (0.0275 mole) of ethyl l,4-dimethylpyrrole-2-acetate in 30 ml. of dry ether is cooled to 5 and a solution of 3.2 g. (0.0325 mole) of phosgene in 50 ml. of ether is added dropwise. The mixture is allowed to stand for 16 hours. The solvent is evaporated in vacuo to give 6.7 g. of white crystalline ethyl 5-chlorocarbonyl-l ,4-dimethylpyrrole-Z-acetate. After the latter is recrystallized from hexane the m.p. is found to be 6566C.

EXAMPLE IV The procedure of Example II is repeated except that an equivalent quantity of methyl l-methypyrrole- 2-acetate is used in place of the ethyl ester used therein to yield, as the respective product, methyl 5- chlorocarbonyl-1-methylpyrrole-Z-acetate.

EXAMPLE V Ethyl l-methyl-5-(p toluoyl)-pyrrole-2-acetate To a solution of 0.0516 mole of p-tolyl magnesium bromide in ether (40 ml.) is added 5.0 g. (0.0274 mole) of cadmium chloride. The mixture is refluxed for 20 minutes, 50 ml. of dry benzene is added and the ether is distilled off. To this solution of di-(p-tolyl) cadmium is added dropwise 5.9 g. (0.0258 mole) of ethyl 5- chlorocarbonyl-l-methylpyrrole-2-acetate in 25 ml. of benzene. The mixture is stirred at room temperature for 1 hour and poured into dilute I-ICl. The mixture is extracted with ether. The ether extract is washed successively with dimethylaminopropylamine solution, dilute I-ICl, and brine and then dried (anhydrous MgSO The solvent is evaporated in vacuo. The residue is crystallized from methyl cyclohexane and recrystallized from ethanol to give white crystalline ethyl lmethyl-S-p-toluoylpyrrole-2-acetate, m.p. 70-71C.

EXAMPLE VI By repeating the procedure of Example V, except that an equivalent amount of methyl S-chlorocarbonyll-methylpyrrole-2-acetate is substituted for the ethyl ester used therein, there is obtained as the final product: methyl l-methyl-5-(p-toluoyl)-pyrrole-2-acetate.

EXAMPLE vn Ethyl l-methyl-5-(p-toluoyl)-pyrrole-2-acetate To a stirred and chilled (60C.) solution of 5.0 g. (0.022 mole) of ethyl 5-chlorocarbonyl-l-methylpyrrole-2-acetate in 300 ml. of dry toluene is added in one portion 0.70 g. (0.0044 mole) of anhydrous FeCl;,, weighed under 5 ml. of toluene and dissolved in 2 ml. of ether. The freshly prepared Grignard solution of 0.023 mole of p-tolylmagnesium bromide in 15 ml. ether is added dropwise, under hydrogen, to the above reaction mixture at such a rate so as to maintain the reaction temperature at 60 i 2C. The mixture is stirred at that temperature for another hour, then hydrolyzed with ice water and made strongly acidic with 3N I-ICl-ice. The aqueous layer is washed three times with benzene and the combined organic layers are washed sequentially with B-dimethylaminopropylamine-ice, 3N HCl-ice, and saturated NaIICO solution. The organic layer is dried over anhydrous MgSO filtered and the solvent evaporated off to give about 2.0 g. (20 percent) of a solid residue with thin layer chromatography (film, silica, 1:3 EtOAc/cyclohexane) showing two major spots (rf 0.54, 0.90). Column chromatography on 50 g. of CC-4 silica and sequential elution with hexane, hexane-benzene, benzene and benzene-ether gives the desired product (eluted with 10 percent Et Olbenzene) as an oil (0.75 g., 12 percent yield). Crystallization from MeOH gives about 350 mg.

.of a white solid, ethyl l-methyl-5-(p-toluoyl)-pyrrole- Z-acetate, m.p. 68-70C.

' EXAMPLE VIII A. Ethyl 5-(p-chlorobenzoyl)-l,4-dimethylpyrrole- 2-acetate To a freshly prepared Grignard solution of 0.055 mole of p-chlorophenyl magnesium bromide in 50 ml. of anhydrous ether is added 5.5 g. (0.030 mole) of cadmium chloride. The mixture is refluxed for 20 minutes, 50 ml. of benzene is added and the ether is distilled off. To this solution of di-(p-chlorophenyl) cadmium reagent is added dropwise a solution of 6.7 g. (0.0275 mole) of ethyl 5-chlorocarbonyl-l,4-dimethylpyrrole- 2-acetate in 50 ml. of benzene. The reaction mixture is stirred at room temperature for another hour and then poured into 3N HCl-ice. The aqueous layer is extracted four times with ether and the combined organic layers are washed sequentially with 3-dimethylaminopropylamine-ice, 3N I-ICl-ice and saturated NaHCO solution. The organics are dried over anhydrous MgSO filtered and then evaporated to give about 7.4 g. of solid residue. Two recrystallizations from MeOI-I gives about 1.8 g. of the product, ethyl 5-(p-chlorobenzoyl)-l ,4- dimethylpyrrole-2-acetate, m.p. l0l-l04C. B. Ethyl S-(p-chlorobenzoyl l -methylpyrrole- Z-acetate The procedure of Example VIII-A is repeated, except that an equivalent amount of ethyl S-chlorocarbonyll methylpyrrole-2-acetate is used as the starting material, to yield as the final product: ethyl 5-(p-chlorobenzoyl)- l-methylpyrrole-2-acetate.

EXAMPLE IX The procedure of Example VIII-A is repeated except that an equivalent amount of methyl S-chlorocarbonyll'-methylpyrrole-2-acetate is used in place of the ethyl ester. used therein to yield, as the respective product,

2-acetate.

EXAMPLE X S-p-Toluoyl-1-methylpyrrole-Z-acetonitrile To a freshly prepared Grignard solution of 0.0516 mold of p-tolyl magnesium bromide in 40 ml. of ether is added 5.0 g. (0.0274 mole) of cadmium chloride. The mixture is refluxed for minutes, 50 ml. of dry benzene is added and the ether is distilled off. To this solution of di-(p-tolyl) cadmium reagent is added dropwise a solution of 4.67 g. (0.0258 mole) of 5- chlorocarbonyl-l-methylpyrrole-2-acetonitrile in ml. of benzene. The reaction mixture is stirred at room temperature for another hour and then poured into 3N I-ICl-ice. The aqueous layer is extracted four times with ether and the combined organic layers are washed sequentially with 3-dimethylamino-propylamine-ice, 3N l-ICl-ice and saturated NaHCO solution. The organics are dried over anhydrous MgSO filtered and then evaporated to give about 3.0 g. (42 percent yield) of an oily residue containing 5-p-toluoyl-l-methylpyrrole-2- acetonitrile, which is isolated by standard column chromatographic techniques.

EXAMPLE XI The procedures of Examples V and VII may be followed to prepare the 5-aroyl esters of formula (I) by appropriate choice of starting materials. For example, by repeating said Examples, except that an equivalent quantity of each of the following known aryl magnesium halides is used as the starting Grignard reagent in place of the p-tolyl magnesium bromide used therein:

phenyl-MgBr,

4-bromophenyl-MgBr,

3,4-dimethoxyphenyl-MgBr,

4-trifluoromethylphenyl-MgBr,

4-methylthiophenyl-MgBr,

3,4-diclilorophenyl-MgCl,

3,5-dimethoxyphenyl, MgCl,

3,4-dimethylphenyl-MgBr, and

4-ethoxyphenyl-MgBr the following respective products are obtained:

ethyl 1-methyl-5-benzoylpyrrole-2-acetate,

ethyl 2-acetate,

ethyl 1-methyl-5-(3 ,4'-dimethoxybenzoyle)-pyrrole- 2-acetate,

ethyl l-methyl-5-(p-trifluoromethylbenzoyle)- pyrrole-2-acetate,

ethyl 1-methyl-5-(p-methylthiobenzoyle)-pyrrole 2-acetate,

ethyl 1-methyl-5-(3,4'-dichlorobenzoyle)-pyrrole- 2-acetate,

ethyl l-methyl-5-(3 ',5'-dimethoxybenzoyle)-pyrrole- 2-acetate,

ethyl l-methyl-5-( 3 ',4'-dimethylbenzoyle)-pyrrole- Z-acetate, and

ethyl l-methyl-5-(p-ethoxybenzoyle)-pyrrole 2-acetate.

EXAMPLE XII The procedure of Example X may be followed to me pare the 5-aroyl nitriles of formula (I) by appropriate choice of starting materials. For example, by repeating l-methyl-5-(p-bromobenzoyle)-pyrrole- Example X, except that an equivalent quantity of each 7 9 the ylmasnss um b m d gimd n. E m X1 is substituted for the p-tolyl magnesium bromide used therein, there are obtained, as respective products, the corresponding 5-aroyll -methylpyrrole-2-acetonitriles of formula (I).

EXAMPLE XIII A. 5-p-Toluoyl-1-methylpyrrole-2-acetic acid A solution of 0.02 mole 5-p-toluoyl-l-methylpyrrole- Z-acetonitrile in 44 ml. In sodium hydroxide and 40 ml. percent ethanol is heated to reflux for 18 hours. The ethanol is then evaporated in vacuo and the remaining solution poured onto ice acidified with dilute HCl. The resulting precipitate is separated by filtration and recrystallized from ether-hexane. The solid is then partitioned between ether and a saturated solution of NaH- C0 The NaHCO fraction is separated and acidified with dilute HCl. The precipitate, S-p-toluoyl-lmethylpyrrole-2-acetic acid, is separated by filtration and purified by recrystallization from ether-methyl cyclohexane solution and dried.

B. By following the nitrile-to-acid hydrolysis procedure of Example XIII-A, except that an equivalent quantity of each nitrile obtained from Example XII is employed as the starting material, the corresponding respective 5-ar0ylpyrrole-2-acetic acids of formula (I) are obtained.

EXAMPLE XIV A. 5-(p-Chlorobenzoyl)-1,4-dimethyopyrrole-2-acetic acid A solution of 0.01 mole of ethyl 5-(p-chlorobenzoyl)- 1,4-dimethylpyrrole-2-acetate in 12 ml. (0.012 mole) of IN sodium hydroxide solution and 5 ml. of 95 percent ethanol is refluxed for 30 minutes. The solution is diluted with water and the ethanol evaporated in vacuo. The remaining solution is filtered and the filtrate acidified with dilute I-ICl. The precipitated solid is collected by filtration and recrystallized from methanol-water to yield the product, 5-(p-chlorobenzoyl)- l,4-dimethylpyrrole-Z-acetic acid.

B. By following the ester-to-acid hydrolysis procedure of Example XIV-A, except that an equivalent quantity of each ester obtained from Examples V, VI, VII and X1 is employed as the starting material, the corresponding respective 5-aroyl-pyrrole-2-acetic acids of formula (I) are obtained.

EXAMPLE XV 5-(p-Chlorobenzoyl)-l-methylpyrrole-Z-acetic acid A solution of 3.06 g. (0.01 mole) of ethyl 5-(pchlorobenzoyl)-1-methylpyrrole-2-acetate in 25 ml. of 0.5 N sodium hydroxide is refluxed for 30 minutes. The solution is cooled, washed with ether and then acidified with dilute HCl. The resulting solid precipitate is collected by filtration, dried and recrystallized from ethanol-water to give the product: S-(pchlorobenzoyl)-l-methylpyrrole-Z-acetic acid, m.p. 189-191C. Upon recrystallization from ethanolwater, the melting point is 188l90C.

I claim:

1. A process of preparing a 5-aroyl-pyrrole-2- alkanoic acid of the formula:

which comprises reacting a S-unsubstituted pyrrole of the formula:

with phosgene in an aprotic solvent in order to prepare a fi-chlorocarbonyl pyrrole of the formula:

Bi. 4 v

to yield the desired 5'aroyl-pyrrole-2-alkanoic acid, wherein the following meanings are assigned to the foregoing symbols:

M is a transition metal selected from the group consisting of copper, zinc and cadmium;

n is an integer equal to the valence of said transition metal;

R is a member selected from the group consisting of hydrogen and lower alkyl; R, is lower alkyl; Z is a member selected from the group'consisting of CN and COO(lower alkyl); and

Ar is a member selected from the group consisting of phenyl and mono-, diand tri-substituted phenyl wherein each substituent is selected from the group consisting of halo, lower alkyl, lower alkoxy, trifluoromethyl and methylthio; provided that, when said R is lower alkyl, then said Z is COO-(lower alkyl).

2. A process of preparing 5-(p-chlorobenzoyl)-1,4- dimethylpyrrole-Z-acetic acid which comprises reacting a lower alkyl 1,4-dimethylpyrrole-Z-acetate with phosgene in an aprotic solvent, treating the thusobtained lower alkyl S-chlorocarbonyl-l,4-dimethylpyrrole-2-acetate with di-(p-chlorophenyl) cadmium in an aprotic solvent, and then hydrolyzing to the acid state the thus-obtained lower alkyl S-(pchlorobenzoyl )-l ,4-dimethylpyrrole-2-acetate.

3. The process of claim 2 wherein the lower alkyl ester function is ethyl.

4. A process of preparing 55-(ptoluoyl)-lmethylpyrrole-Z-acetic acid which comprises reacting a lower alkyl l-methylpyrrole-2-acetate with phosgene in an aprotic solvent, treating the thus-obtained lower alkyl 5-(p-chlorobenzoyl)-l-methylpyrrole-2-acetate with di-(p-tolyl) cadmium in an aprotic solvent, and then hydrolyzing to the acid stage the thus-obtained lower alkyl 5-(p-toluoyl)-1-methylpyrrole-2-acetate.

5. The process of claim 4 wherein the lower alkyl ester function is ethyl.

6. A process of preparing a 5-aroyl-pyrrole derivative of the formula:

which comprises reacting a S-unsubstituted pyrrole of the formula:

with phosgene in an aprotic solvent in order to prepare a S-chlorocarbonyl pyrrole of the formula:

treating the latter with a member selected from the group consisting of (i) an aryl transition metal compound of the formula: (Ar),,M, and (ii) an aryl Grignard reagent of the formula: ArMgBr, in the presence of a catalytic amount of a transition metal halide selected from the group consisting of ZnCl CdCl FeCl CoCl and (CuBr) in order to transform said 5- chlorocarbonyl function into a S-Ar-CO function, wherein the following meanings are assigned to the foregoing symbols:

M is a transition metal selected from the group consisting of copper, zinc and cadmium; n is an integer equal to the valence of said transition metal; R is a member selected from the group consisting of hydrogen and lower alkyl; R is lower alkyl; 2 is a member selected from the group consisting of CN and COO(lower alkyl); and Ar is a member selected from the group consisting of phenyl and mono-, diand tri-substituted phenyl wherein each substituent is selected from the group consisting of halo, lower alkyl, lower alkoxy, trifluoromethyl and methylthio; provided that, when said R is lower alkyl, then said Z is COO(lower alkyl).

7. A process of preparing a lower alkyl S-(pchlorobenzoy1)- l ,4-dimethylpyrrole-2-acetate which comprises reacting a lower alkyl 1,4-dimethylpyrrole- Z-acetate with phosgene in an aprotic solvent, and treating the thus-obtained lower alkyl 5- chlorocarbonyl-l,4-dimethylpyrrole-Z-acetate with di- (p-chlorophenyl) cadmium in an aprotic solvent.

8. The process of claim 7 wherein the lower alkyl ester function is ethyl.

9. A process of preparing a lower alkyl 5-(p-toluoyl)- 1-methylpyrrole-2-acetate which comprises reacting a lower alkyl l-methylpyrrole-2-acetate with phosgene in an aprotic solvent, and treating the thus-obtained lower alkyl 5-chlorocarbonyl 1-methylpyrrole-2-acetate with di-(p-tolyl) cadmium in an aprotic solvent.

10. The process of claim 9 wherein the lower alkyl ester function is ethyl.

11. A process of preparing a 5-chlorocarbonylpyrrole of the formula:

which phosgene in an inert aprotic solvent, wherein the following meanings are assigned to the foregoing symbols:

R is a member selected from the group consisting of hydrogen and lower alkyl;

R, is lower alkyl; and

Z is a member selected from the group consisting of CN and COO(lower alkyl); provided that, when said R is lower alkyl, then said Z is COO(lower alkyl).

12. A process of preparing S-chlorocarbonyl-lmethylpyrrole-2-acetonitrile which comprises reacting l-methylpyrrole-2-acetonitrile with phosgene in an aprotic solvent.

13. A process of preparing ethyl S-chlorocarbonyl-lmethylpyrrole-Z-acetate which comprises reacting ethyl-l-methylpyrrole-2-acetate with phosgene in an aprotic solvent.

14. A process of preparing ethyl S-chlorocarbonyl- 1,4-dimethylpyrrole-2-acetate which comprises reacting ethyl l,4-dimethylpyrrole-2-acetate with phosgene in an aprotic solvent.

15. A process of preparing methyl 5-chlorocarbonyll-methylpyrrole-2-acetate which comprises reacting methyl l-methylpyrrole-2-acetate with phosgene in an aprotic solvent.

73 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, A 7 Dated November 5,l97

Inventor(s) John Robert Carson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In References Cited, Reference 1 should read Mozheiko et al. Chem.Aos. 69; 28725 (1968), of USSR Pat. 21h,307.

In Column 2, line 17, after the word "and" insert the phrase like, at

In Column 2, formula 3, should be In Column 3, line 3",, "l-me'thypyrrole-" should read l-methylpyrrole-- In Coluzrm 6, line 9, "In sodium hydroxide" should read 1N sodium hydroxide In Column 8, line I, The repetition of the numeral "5" is erroneous. The line should read A process of preparing 5- (p-toluoyD-l- In Column 10, line 8, "which" should read with Signed and sealed this 22nd day of April 1975.

(SEAL) Attest:

C MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks 

1. A PROCESS OF PREPARING A 5-AROYL-PYRROLE-2-ALKANOIC ACID OF THE FORMULA:
 2. A process of preparing 5-(p-chlorobenzoyl)-1,4-dimethylpyrrole-2-acetic acid which comprises reacting a lower alkyl 1,4-dimethylpyrrole-2-acetate with phosgene in an aprotic solvent, treating the thus-obtained lower alkyl 5-chlorocarbonyl-1,4-dimethylpyrrole-2-acetate with di-(p-chlorophenyl) cadmium in an aprotic solvent, and then hydrolyzing to the acid state the thus-obtained lower alkyl 5-(p-chlorobenzoyl)-1,4-dimethylpyrrole-2-acetate.
 3. The process of claim 2 wherein the lower alkyl ester function is ethyl.
 4. A process of preparing 55-(p-toluoyl)-1-methylpyrrole-2-acetic acid which comprises reacting a lower alkyl 1-methylpyrrole-2-acetate with phosgene in an aprotic solvent, treating the thus-obtained lower alkyl 5-(p-chlorobenzoyl)-1-methylpyrrole-2-acetate with di-(p-tolyl) cadmium in an aprotic solvent, and then hydrolyzing to the acid stage the thus-obtained lower alkyl 5-(p-toluoyl)-1-methylpyrrole-2-acetate.
 5. The process of claim 4 wherein the lower alkyl ester function is ethyl.
 6. A process of preparing a 5-aroyl-pyrrole derivative of the formula:
 7. A process of prEparing a lower alkyl 5-(p-chlorobenzoyl)-1,4-dimethylpyrrole-2-acetate which comprises reacting a lower alkyl 1,4-dimethylpyrrole-2-acetate with phosgene in an aprotic solvent, and treating the thus-obtained lower alkyl 5-chlorocarbonyl-1,4-dimethylpyrrole-2-acetate with di-(p-chlorophenyl) cadmium in an aprotic solvent.
 8. The process of claim 7 wherein the lower alkyl ester function is ethyl.
 9. A process of preparing a lower alkyl 5-(p-toluoyl)-1-methylpyrrole-2-acetate which comprises reacting a lower alkyl 1-methylpyrrole-2-acetate with phosgene in an aprotic solvent, and treating the thus-obtained lower alkyl 5-chlorocarbonyl 1-methylpyrrole-2-acetate with di-(p-tolyl) cadmium in an aprotic solvent.
 10. The process of claim 9 wherein the lower alkyl ester function is ethyl.
 11. A process of preparing a 5-chlorocarbonyl-pyrrole of the formula:
 12. A process of preparing 5-chlorocarbonyl-1-methylpyrrole-2-acetonitrile which comprises reacting 1-methylpyrrole-2-acetonitrile with phosgene in an aprotic solvent.
 13. A process of preparing ethyl 5-chlorocarbonyl-1-methylpyrrole-2-acetate which comprises reacting ethyl-1-methylpyrrole-2-acetate with phosgene in an aprotic solvent.
 14. A process of preparing ethyl 5-chlorocarbonyl-1,4-dimethylpyrrole-2-acetate which comprises reacting ethyl 1,4-dimethylpyrrole-2-acetate with phosgene in an aprotic solvent.
 15. A process of preparing methyl 5-chlorocarbonyl-1-methylpyrrole-2-acetate which comprises reacting methyl 1-methylpyrrole-2-acetate with phosgene in an aprotic solvent. 